New Delhi: A special CBI court in Mumbai has issued non-bailable warrants against billionaire diamantaire Nirav Modi and his uncle Mehul Choksi in connection with the Punjab National Bank fraud, officials said here on Sunday.

The court has allowed the investigative agency's application for issuing the warrants against Modi and Choksi who have repeatedly refused to join the probe into the scam, considered the biggest in the country's banking history, the officials said.

The agency had written to both on their official email IDs but they have refused to join the investigations citing business engagements and health issues.

The warrants also open the door to seeking red-corner notices from Interpol against the two.

The government claims to have tracked Modi in Hong Kong where it has sent a request for his provisional arrest.

The CBI is questioning officials of overseas branches of Indian banks that had extended credit facilities to the companies of Modi and Choksi on the basis of fraudulent letters of undertaking (LoUs) issued by PNB's Brady House branch in Mumbai. The agency has also summoned an official who handled foreign exchange transactions in the Hong Kong branch of Allahabad Bank.

It is alleged that the LoUs and letters of credit (LCs), worth close to $2 billion, were issued to the companies of the uncle and nephew from the Brady House branch through SWIFT (Society for Worldwide Interbank Financial Telecommunication) messages. The messages were allegedly not entered in PNB's banking software to bypass surveillance. Several bank employees have been booked for collusion in the case.

Modi, a regular feature on the lists of rich and famous Indians since 2013, was booked by the CBI, along with his wife, brother and Choksi for allegedly cheating the state-run PNB. Uncle and nephew fled the country in the first week of January, days before PNB was able to detect the fraud.